usb: ehci-generic: don't probe fail if there is no clk_enable() ops

Some clock driver do not have a clk_enable() call back, and we should not
treat this as fail in ehci probe like other modules, eg. clk_enabl_bulk()
do not return fail if ret value is '-ENOSYS'

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>

drivers/usb/host/ehci-generic.c

@@ -96,7 +96,7 @@ static int ehci_usb_probe(struct udevice *dev)
 			if (err < 0)
 				break;
 			err = clk_enable(&priv->clocks[i]);
-			if (err) {
+			if (err && err != -ENOSYS) {
 				dev_err(dev, "failed to enable clock %d\n", i);
 				clk_free(&priv->clocks[i]);
 				goto clk_err;